A communications system having a plurality of communications users and a plurality of coupling networks that are allocated to a respective communications user is known from the related art. Here, a transmission channel for the communications system is made up of two supply lines, via which a unit is connected to a consumer in order to supply the consumer with electrical energy. Each coupling network is connected to a respective other supply line of the supply lines using one of two input-side connections in each case. In addition, each coupling network is connected to the allocated communications user via two output-side connections. The coupling networks are provided to couple or decouple communications signals into or from the supply lines.
Voltages that occur on the supply lines are usually very high and are therefore not directly usable by the communications users (communications nodes). Depending on an application type of the communications system, these voltages can amount to several hundred volts. Signal voltages of the communications signals that occur during a data transmission between the communications users amount to only a few millivolt in most instances. In special cases, these signal voltages can also lie in the single digit voltage range. To allow for a safe operation of the communications system, a galvanic separation is therefore ensured between the input and the output connections of each coupling network, i.e., between a transmitter and receiver unit of each communications user and the transmission channel. Such a galvanic separation can be achieved inductively via transformers or capacitively via capacitors. In practice, such a galvanic separation usually takes place through a combination of transformers and capacitors.
Because of characteristics of the transmission channel and the data rates required during the data transmission, complex modulation and encoding methods are required in a previously mentioned communications systems. As a rule, these utilize a frequency range of several megahertz. Abrupt changes in the impedance, which lead to reflections of the communications signals that occur in the data transmission, are encountered at these frequencies, especially at the ends of the transmission channel. These reflections lead to a change in the communications signals and can cause that a decoding of the communications signals, i.e., a retrieval of information contained in the communications signals, is no longer possible on the receiver side. To reduce said changes in the communications signals, each coupling network is employed to adapt an impedance (AC current resistance) of the allocated communications user that occurs during the data transmission to the impedance of the transmission channel.